$ax^2 + bx + c = 0$
$(px + q)(rx + s) = 0$
$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$
The graph below shows a quadratic equation. Control the $a$, $b$ and $c$ parameters by moving the sliders at the bottom of the graph. The points at which the curve crosses the X axis are calculated beneath the graph.